Electrical high voltage apparatus equipped with a movable air lock device for exchanging the filament of an electron gun

ABSTRACT

An electric high-voltage apparatus such as an electron accelerator or the like includes a tank having a wall and a tank access located in the wall for making the interior of the tank accessible. An electrical discharge vessel is disposed in the tank and contains replaceable parts. The vessel has a wall and is insulatingly spaced from the tank wall. A vessel access is located in the vessel wall for making the replaceable parts accessible. A tube-like air lock device having a longitudinal axis is movable in the tank transversely to this axis from a given rest position to an operative position located between the tank access and said vessel access. The device includes expansion structure for defining a gas-tight passage between the vessel access and the tank access when the device is in the operative position thereof.

ilnited States Patent Stocklein 1 1 Mar. 27, 1973 ELECTRICAL HIGHVOLTAGE APPARATUS EQUIPPED WITH A MOVABLE AIR LOCK DEVICE FOR EXCHANGINGTHE FILAMENT OF AN ELECTRON GUN Appl. No.: 224,789

Foreign Application Priority Data Feb. 26, 1971 Germany ..P 21 10 [30.4

US. Cl ..313/237 Int. Cl. ..H0lj l/OO, HOlj 1/92 Field of Search..3l3/236, 237

References Cited UNITED STATES PATENTS Sakamoto .313 23'7 PrimaryExaminer-David Schonberg Assistant Examiner-Paul A. SacherAtt0rneyArthur E. Wilfond et al.

[57] ABSTRACT An electric high-voltage apparatus such as an electronaccelerator or the like includes a tank having a wall and a tank accesslocated in the wall for making the interior of the tank accessible. Anelectrical discharge vessel is disposed in the tank and containsreplaceable parts. The vessel has a wall and is insulatingly spaced fromthe tank wall. A vessel access is located in the vessel wall for makingthe replaceable parts accessible. A tube-like air lock device having alongitudinal axis is movable in the tank transversely to this axis froma given rest position to an operative position located between the tankaccess and said vessel access. The device includes expansion structurefor defining a gas-tight passage between the vessel access and the tankaccess when the device is in the operative position thereof.

14 Claims, 5 Drawing Figures PATENTEU MR2? i973 SHEET 3 [IF Theapparatus is equipped with a movable tubular air lock which makes itpossible to establish a passage between respective closable openings inthe tank wall and the vessel wall. The passage is sealed against thesewalls and the vacuum or the protective gas filling. The passage affordsaccess to components of the discharge vessel for replacing the same.

The invention is especially adaptable for an electron accelerator whichcan for instance serve as the beam source for an electron microscope.Here, the requirement exists to pass through the walls of the dischargevessel and the tank and remove and replace the cathode which is locatedin the discharge vessel. So that the gas filling or the vacuum can bemaintained in the tank during this replacement procedure, a tubular airlock is used which is moved between the openings of the discharge vesseland the tank.

Such an arrangement is known, for instance, from the German publishedPatent application No. 1,205,208. Here the tubular air lock is moved inthe direction of its axis. In the rest position, the air lock is locatedoutside of the tank on upper side of the latter. The space required forthe arrangement is therefore increased in the vertical direction.Furthermore, the sealing of the tubular air lock is made more difficultby the requirement that the air lock must be movably slidable in itsguide structure.

Accordingly, it is an object of the invention to provide an electricalhigh voltage apparatus equipped with a movable air lock device whichovercomes the disadvantages of the above-referred to prior artapparatus.

It is also an object of the invention to provide an electrical highvoltage apparatus equipped with a movable air lock device which is ofcompact configuration and affords a reliable gas-tight access to partscon tained in the apparatus.

According to a feature of the invention, a tubular air lock is situatedwithin the tank of a high voltage apparatus of the type mentioned above.The air lock remains within the tank during the operation of thedischarge vessel. The air lock device has a longitudinal axis and ismovable into the transfer or operative position in a directiontransversely to this axis. The air lock device includes expansion meansfor defining a gastight passage between an access means located in thewall of the tank and an access means in the wall of the vessel when theair lock device is in the operative position. The gas-tight seal isformed with the sealing surfaces of the vessel and the tank sealingflanges of the expansion means. The invention affords the advantage thatno additional structural height is required for the tubular air locksince it is always located in the tank. In addition, the sealing of thetubular air lock against the walls of the tank and the discharge vesselis substantially simplified because the sealing means are merely pressedagainst each other and are therefore not stressed with sliding frictionand shear.

The tubular air lock device can include an expandable member in the formof a metal bellows. However, the expandable member can also beconfigured in the form of tubular members telescopically joined onewithin the other. The expansion means of the air lock device can includelinkage means having a knee lever which in the operative positionextends beyond dead center position. The knee lever comprises elongatedmembers which are pivotally joined at a pivot connection to form anacute angle. Each of the elongated members has an end pivotallyconnected to the expandable member, and means are provided for movingthe linkage members angularly with respect to each other at theoperative position so that the pivot connection moves laterally throughthe dead center position of knee lever to cause the acute angle tobecome an obtuse angle. The knee lever can act upon threaded rings whichare attached at the sealing flanges and which are adjustable. Thethreaded rings make it possible to adapt the spacing of the sealingflanges to the spacing between the respective sealing surfaces of thetank and the vessel.

The linkage means of the tubular air lock device advantageously includesa set of rails upon which a carriage moves for carrying the expandablemember. A drive means is operatively connected to the carriage formoving it and the expandable member laterally to the operative position.The carriage includes means operatively connected to the drive means andto the knee lever for extending the expandable member at the operativeposition in response to a further actuation of the drive means. In thisway, it is possible to move the tubular air lock into the operativeposition as well as to expand it with a single driving operation. Thesame applies for the reverse procedure, namely, removing the tubular airlock device from the operative position and returning it to its restposition. In this connection, it is furthermore advantageous to provideresilient means in the form of springs which act in the sense of foldingthe knee lever; this makes it easier for expandable member of thetubular air lock device to become shorter, for instance, because of itsown longitudinal elasticity. The same or correspondingly acting separatesprings can, however, also act upon the sealing flanges in the sense ofshortening the expandable member and thereby draw the sealing flangesaway from the sealing surfaces of the tank and the discharge vessel whenthe tubular air lock is moved away from the operative position. A detentcan be provided which holds the tubular air lock in the operativeposition at the start of its return until the sealing flanges haveseparated safely from the sealing surfaces.

During the operation of the vessel, the tubular air lock may be situatedin any given part of the tank at which it disturbs the fielddistribution between the tank and the discharge vessel as little aspossible. Preferably there is provided in the tank a lateral pocket orenclosure which receives the tubular air lock during the operation ofthe vessel. This pocket is closed off advantageously by a metal platewhen the tubular air lock is moved into the pocket, so that the innerwall of the tank has no projecting parts which would cause discharges.

Each time the air lock is moved to the operative position and used, aloss of protective gas occurs which corresponds to the free volume ofthe tubular air lock. This loss can be largely reduced by inserting aremovably insertable filler body into the tubular lock whichsubstantially fills the volume of the tubular lock.

Although the invention is illustrated and described herein as electricalhigh voltage apparatus equipped with a movable air lock device, it isnevertheless not intended to be limited to the details shown,:sincevarious modifications may be made therein within the scope and the rangeof the claims. The invention, however, together with additional objectsand advantages will be best understood from the following descriptionand in connection with the accompanying drawings in which:

FIG. 1 is an elevation view, in section, of an electron acceleratorequipped with a tubular air lock shown in the rest position;

FIG. 2 an elevation view of the electron accelerator of FIG. 1 showingthe tubular air lock in the transfer position;

FIG. 3 is a plan view of the tubular air lock and its guidance memberswith the cover of the vessel removed; and,

FIG. 4 is a side view of the tubular air lock guidance members takenalong line lVlV of FIG. 3; and,

FIG. 5 is another embodiment of the air lock.

In FIGS. 1 and 2, the wall of the discharge vessel is designated withreference numeral 1. The wall 1 con sists of insulating material such asceramic. The discharge vessel is closed off in a vacuum-tight manner bymeans of a metal lid 2 which carries the cathode 3. Above the cathode,vessel access means comprising an opening in the lid 2 and a threadedinsert 4 that closes off the opening vacuum tight is provided.

The discharge vessel is located in a metal tank 5 which is closed by alid 6 in a pressuretight manner. The lid 6 of the tank has tank accessmeans comprising an opening above the cathode 3 and an insert 7 whichcloses the opening vacuum-tight. The space 8 between the dischargevessel 1, 2 and the tank 5, 6 is filled with an electro-negative gas,for instance, sulfur hexafluoride, SF at a pressure of 4 atmospheres.During operation of the discharge vessel, the lid 2 with the cathode 3is at high negative potential, for instance, several hundred kilovolts,while the tank 5, 6 is at ground potential.

In order to replace the cathode 3, the inserts 4 and 7 must be removedwhile maintaining the gas filling in the space 8 as far as possible.

For this purpose, an expandable tubular air lock member designated byreference numeral 9 is provided, which in the illustrated embodiment isconfigured as a metal bellows that can expand along its longitudinaldirection. The tubular air lock 9 is provided at the upper and loweredge with sealing flanges l0 and II, respectively. Seal rings 12 and 13are inserted into flanges l0 and 11 respectively, and are pressedagainst the sealing surfaces 14 and 15 of the tank lid 6 and the lid 2of the discharge vessel in the transfer or operating position as shownin FIG. 2. At each sealing flange is attached a threaded ring 16 and I7,respectively. Pressure rings 18 and 19 engage the threaded rings 16 and17 which are pushed apart by two k'riee levers 20a and 20b when thetubular air lock is moved into the transfer position; this action isexplained later in more detail. In this way, the sealing flanges 10 and11 are pushed via the threaded rings 16 and 17 against the lid 2 of thedischarge vessel and the lid 6 of the tank, this being especiallyevident in FIG, 2. By turning the threaded rings 16 and 17, the spacingof the sealing flanges 10 .and 11 can be matched to the spacing betweenthe lid of the discharge vessel 2 and the tank lid 6 in such a mannerthat the sealing rings 12 and 13 are under a suitable pressure in thetransfer position. Tension springs 21 and 22 are located between thepressure rings 18 and 19 which cause the knee levers 20a and 20b to foldand thereby initiate the shortening of the tubular airlock when it ismoved away from the operating position.

As may be seen particularly from FIGS. 1, 3 and 4, the tubular air lock9 is supported on a carriage 23, which is movable in a directionperpendicular to the axis of the tubular air lock. The knee levers 20aand 20b are linked to this carriage 23 and are connected by joints attheir outer ends to the pressure rings 18 and 19. The carriage 23 runson two guide rails 24 and 25 by means of support rails 26 and 27 ofwhich one (27) is configured as a toothed rack member. For drivingthecarriage 23, a pinion 28 is provided which engages with the rack 27 andcan be operated from the outside by a crank 29.

In the tubular air lock 9, there is located a removable filler 30 whichlargely fills the volume of the air lock.

The drive for moving the carriage 23 with the tubular airlock 9 operatesas follows:

According to FIG. 1, the carriage 23 is in its rest position in anenclosure in the form of a lateral pocket 5a of the tank wall 5. Thepocket 5a is here closed on the inside by a metal plate 31 which isconnected with the carriage 23. If the crank 29 is now turned, thecarriage 23 slides on the guide rails 24 and 25 to the left into theoperating position. Upon reaching the operating position, the pressurerings 18 and 19 with projections 18a and 19a, respectively, meet thefixed counter surfaces 32, 33 of the tank lid 6 and the vessel lid 2respectively. These stops prevent a further movement of the tubular airlock 9 perpendicular to its axis. Upon further rotation of the crank 29,the carriage 23 moves further to the left and, with the tubular air lock9 held fixed, the knee levers 20a and 20b are now spread and the sealingflanges l0 and 11 are tensioned via the pressure rings 18 and 19 againstthe sealing surfaces 14, 15 of the tank lid 6 and the vessel lid 2respectively. The knee levers 20a and 20b are here pushed beyond deadcenter so that they exert no return force on the transfer gear. Theirend position is defined by a projection 23a of the carriage 23 whichmakes contact with the pressure ring 18; this position is shown in FIG.2. The range of displacement of the carriage 23 between the arrest ofthe tubular air lock 9 in the transfer position and the' impact of thecarriage at the pressure ring 18 is noted by a slight increase of thetorque at the crank 29. The end of the movement can clearly be felt bythe hard stop.

Referring to FIG. I, the center joints of the knee levers 20a and 20bare supported on the carriage 23 in such a way that there is clearancein the direction of the tubular air lock axis. In this way,lack ofparallelism (perpendicular to the plane of the drawing of FIGS. 1 and2)between the tank and vessel lids as well as between these lids and thecarriage 23 is compensated for. Furthermore, this manner of supportensures that the same pressure automatically adjusts itself at the upperand lower seal.

With this, the move of the tubular air lock into the transfer positionis completed. Now the insert 7 can be removed from the tank lid 6 andthe filler can be removed from the tubular air lock 9. With thisf andafter destroying the vacuum in the discharge vessel, the insert 4 can bethreadedly disengaged from the tank lid 2 so that the cathode 3 isaccessible and can be exchanged by means of a suitable tool.

After closing the air lock in the reverse sequence, the tubular air lockis run back into its rest position by turning the crank 29 in theopposite direction. At the beginning of this movement, tubular air lock9 is at first held in the operating position by the adhesion of thesealing rings 12 and 13 at the sealing surfaces 14 and 15. The carriage23 moves away from the tubular air lock 9 to the right and pulls theknee arms 20a and 20b beyond dead center. The distance between thepressure rings 18 and 19 is shortened under the influence of the tensionsprings 21, 22. The tubular air lock 9 is also allowed to become shorterthereby under the influence of the longitudinal spring loading, andafter leaving the self-locking range in the knee lever linkage, thepressure rings 18 and 19 make contact with the carriage 23. The sealingrings 12 and 13 have then separated from the respective sealing surfaces14 and 15. The parts can also be so disposed that the tension springs21, 22, in addition to acting on the pressure rings 18 and 19, also acton the sealing flanges l0 and 11 in the sense of shortening the tubularair lock 9, for instance, by providing corresponding stops between thepressure rings 18 and 19 on the one hand, and the sealing flanges 10 and11 on the other hand.

By further turning the crank 29 in the same sense, the carriage 23 withthe tubular air lock 9 is then run into the pocket by 5a. The pocket 5ais closed by the plate 31 in such a manner that the inner surface of thetank 5 has an essentially smooth surface at this location.

FIG. 5 illustrates another embodiment of the expandable tubular airlock. it consists of two tubes 34 and 35 mutually telescoped which aresealed with respect to each other. The sealing flanges are againdesignated by reference numerals l0 and 1 l.

in the shown example of an embodiment according to FIGS. 1 to 4, thetubular air lock moves in a rectilinear direction. The invention is notlimited to this form of motion; for instance, a rotating motion withcircular-arc guidance can be provided. This motion of the tubular airlock is also perpendicular to its axis.

Iclaim:

1. Electric high-voltage apparatus such as an electo said axis from agiven rest position to an operative position located between said tank}access means and said vessel access means, said device comprisingexpansion means for defining a gas-tight passage between said vessel.access means and said tank access means when said device is in saidoperative position thereof.

2. The apparatus of claim 1, said vessel wall being insulated from saidtank wall by a protective gas.

3. The apparatus of claim 1, said vessel wall being insulated from saidtank wall by a vacuum.

4. The apparatus of claim 1 comprising sealing surfaces formed on saidwalls respectively in surrounding relation to corresponding ones of saidaccess means, and said expansion means comprising an expandable memberhaving sealing flanges at respective ends thereof, and linkage meansconnected to said expandable member for extending the latter to presssaid sealing flanges gas-tight against said sealing surfacesrespectively.

5. The apparatus of claim 4, said expandable member being a tubularmetal bellows.

6. The apparatus of claim 4, said expandable member being at least twotubular members telescopically connected with each other.

7. The apparatus of claim 4, said linkage means comprising a knee leverhaving elongated members pivotally joined with each other at a pivotconnection to form an acute angle, each of said elongated members havingan end pivotally connected to said expandable member, and means formoving said linkage members angularly with respect to each other at saidoperative position so that the pivot connection moves laterally to causesaid acute angle to become an obtuse angle.

8. The apparatus of claim 7, said expandable member having ringsthreadably engaging respective ones of said sealing flanges foradjusting the positions of the latter, said elongated members being inoperative connection with said rings.

9. The apparatus of claim 7, said linkage means comprising a set ofrails, and a carriage mounted on said rails for carrying said expandablemember, and a drive means connected to said carriage for moving saidcarriage and said expandable member laterally from said rest position tosaid operative position, said carriage including means operativelyconnected to said drive means and to said knee lever for extending saidexpandable member at said operative position in response to a furtheractuation of said drive means.

10. The apparatus of claim 7, said device comprising resilient meansconnected to opposite end portions of said expandable member and actingin a direction to fold said knee lever.

11. The apparatus of claim 10, said resilient means being springs.

12. The apparatus of claim 1, said tank being formed with a lateralenclosure for accommodating said air lock device in said rest position.

13. The apparatus of claim 9, said tank being formed with a lateralenclosure for accommodating said air lock device in said rest position,said carriage having a metal plate for closing said enclosure when saidair lock device is in said rest position.

14. The apparatus of claim 4, comprising a filler

1. Electric high-voltage apparatus such as an electron acceleratorcomprising a tank having a wall, tank access means located in said wallfor making the interior of said tank accessible, an electrical dischargevessel disposed in said tank and containing replaceable parts, saidvessel having a vessel wall and being insulatingly spaced from said tankwall, vessel access means located in said vessel wall for making thereplaceable parts accessible, and a tube-like air lock device having alongitudinal axis, said device in assembled condition always beingpositioned entirely within said tank, and means for moving said devicein said tank transversely to said axis from a given rest position to anoperative position located between said tank access means and saidvessel access means, said device comprising expansion means for defininga gas-tight passage between said vessel access means and said tankaccess means when said device is in said operative position thereof. 2.The apparatus of claim 1, said vessel wall being insulated from saidtank wall by a protective gas.
 3. The apparatus of claim 1, said vesselwall being insulated from said tank wall by a vacuum.
 4. The apparatusof claim 1 comprising sealing surfaces formed on said walls respectivelyin surrounding relation to corresponding ones of said access means, andsaid expansion means comprising an expandable member having sealingflanges at respective ends thereof, and linkage means connected to saidexpandable member for extending the latter to press said sealing flangesgas-tight against said sealing surfaces respectively.
 5. The apparatusof claim 4, said expandable member being a tubular metal bellows.
 6. Theapparatus of claim 4, said expandable member being at least two tubularmembers telescopically connected with each other.
 7. The apparatus ofclaim 4, said linkage means comprising a knee lever having elongatedmembers pivotally joined with each other at a pivot connection to forman acute angle, each of said elongated members having an end pivotallyconnected to said expandable member, and means for moving said linkagemembers angularly with respect to each other at said operative positionso that the pivot connection moves laterally to cause said acute angleto become an obtuse angle.
 8. The apparatus of claim 7, said expandablemember having rings thrEadably engaging respective ones of said sealingflanges for adjusting the positions of the latter, said elongatedmembers being in operative connection with said rings.
 9. The apparatusof claim 7, said linkage means comprising a set of rails, and a carriagemounted on said rails for carrying said expandable member, and a drivemeans connected to said carriage for moving said carriage and saidexpandable member laterally from said rest position to said operativeposition, said carriage including means operatively connected to saiddrive means and to said knee lever for extending said expandable memberat said operative position in response to a further actuation of saiddrive means.
 10. The apparatus of claim 7, said device comprisingresilient means connected to opposite end portions of said expandablemember and acting in a direction to fold said knee lever.
 11. Theapparatus of claim 10, said resilient means being springs.
 12. Theapparatus of claim 1, said tank being formed with a lateral enclosurefor accommodating said air lock device in said rest position.
 13. Theapparatus of claim 9, said tank being formed with a lateral enclosurefor accommodating said air lock device in said rest position, saidcarriage having a metal plate for closing said enclosure when said airlock device is in said rest position.
 14. The apparatus of claim 4,comprising a filler piece removably insertable into said expandablemember.